Antenna system



M. KA-rzlN 2,303,644

ANTENNASYSTEM Filed March 12, 1941 Dec. l, 1942.

Patented Dec. 1, 1942 AN IENNA SYSTEM Martin Katzin, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application March 12, 1941, Serial No. 382,848

(Cl. Z50-20) 9 Claims.

'Ihis invention relates to improvements in ultra high frequency receiving systems for receiving waves in the range above 30 megacycles.

In communication withwaves of the order of 30 megacycles and less, the path of travel between a radio transmitter and a remote receiver is mainly by reflection from the ionosphere. At frequencies generally above 30 megacycles or so, however, the ionosphere is no longer capable of reflecting waves of such high frequencies, and communication is effected mainly by means of the direct or ground wave. One source of signal variation is that due to changes in the strength of the signal as received from the signal medium. In the case of radio reception, such variations are generally known as fading Studies of the type of fading occurring at frequencies above 30 megacycles with which the present in- Vention is primarily concerned, have shown that the fading is due to variation of the electrical characteristics of the lower atmosphere. These variations may be of two general types. type produces a change in the refractive constants of the medium, as a consequence of which the magnitude of the received signal varies slowly; that is, there occurs a fading prenomenon. 'I'he other type of fading is produced' by sudden discontinuities or changes in the characteristics of the lower atmosphere or troposphere, such as occur between overlying air masses. These overlying air masses usually occur at rather low altitudes of the order of 1 kilometer or so. Such sudden discontinuities produce, in effect, a wave reflecting stratum in the atmosphere which may deflect towards the ground some of the radiation that would normally escape skyward. Thus, in addition to the direct or round wave, another wave may arrive at the receiver which in many respects is the equivalent of the sky wave normally received at lower frequencies from the ionosphere. This additional wave which is reflected by the lower atmosphere, and which we may refer to as a sky wave, combines with the ground wave at the receiver to produce the resultant received signal wave. The magnitude of the resultant signal wave depends on the resultant amplitudes and phase relations of both the ground wave and the sky wave produced by the atmospheric discontinuities. This sky wave, which is produced by the atmospheric discontinuities, should not, however, be confused with the ionosphere sky wave, because of the fact that the ionosphere is not capable of reflecting the waves of the higher frequencies with which the present in- .reiiected from the ionosphere.

vention is primarily concerned. Under certain conditions, the relations between the ground wave and the sky waves produced by the atmospheric discontinuities may be such that they substantially annul each other at the receiver, thus producing what is generally known as a fade out or a substantially complete interruption of the received signal. Such a fade out, it has been observed, may last from about one minute up to about fifteen minutes, thus rendering the circuit inoperative for this duration.

An object of the present invention is to overcome the signal variation caused by the sky wave in a communication system employing frequencies above 30 megacycles.

Another object is to provide a radio receiving system of high elciency which overcomes substantially completely the possibility of the signal fading out at the receiver by virtue of atmospheric discontinuities when communication is effected at frequencies above 30 megacycles.

In brief, the invention is based on the fact that if a number of signal collectors (antennas) are properly located in a vertical direction, above one another and sufficiently spaced apart to pick up a transmitted signal, the signal will not fade similarly at each of these signal pick-ups. The possibility of the signal fading out equally at all of these vertically spaced signal collectors or antennas at the same time is obviously reduced with increase in the number of receiving signal collectors or antennas. It is preferred that these receiving signal collectors be spaced from one another in a vertical direction by a i. plurality of wavelengths (at least ten wavelengths). If desired, the signal collectors may be spaced directly above one another cn the same mast, or, if desired, spaced somewhat apart from each other horizontally as well.

Although it has heretofore been proposed to overcome fading by spacing apart a plurality of receiving antennas in the horizontal direction, in order to obtain a diversity receiving system, it should be understood that systems of this known kind are concerned with an altogether different type of fading than that with which the present invention is concerned. The known receiver diversity system just mentioned, is employed in systems using the lower frequencies which are Such known systems are vastly different from the vertical spacing or diversity system which I propose and are not capable of overcoming the type of .fading present on'the higherV frequencies with which th present invention is concerned..

A more detailed description of the invention follows in conjunction with a single drawing, which shows, by way of example only, a receiving system embodying the principles of the present invention,

Referring to the drawing, there is shown a receiver system employing two vertically spaced signal collectors I and 2 mounted on a suitable Supporting mast 3. Signal collectors I and 2 are shown as electromagnetic horn antennas, generally of the type described in my copending applications Serial Nos. 354,954, filed August 31, 1940; 363,248, led October 29, 1940; 369,826, filed December 12, 1940, although it should be distinctly understood that these signal collectors may be dipoles or any other suitable type of antennas. Although only two receiving antennas have been shown, it should be understood that any greater number of antennas maybe employed, the only requirement being that they be spaced apart from one another in the vertical direction by at least several wavelengths, Further, it is not essential that the signal collectors be of the same type, since one or more different types or arrays can be employed at the same time. For example, signal collector I might be a dipole or an array of dipoles, or a parabolic reflector antenna, or an electromagnetic horn, as shown, while signal collector 2 might be any one of the foregoing types. As for the supporting mast 3, this might be a metallic mast or a wooden mast, or any other suitable supporting structure such as a building or a pole.

Antennas I and 2 are shown individually cou-Y pled by way of transmission lines 4 and 5 to individual receivers 6 and 1, respectively, whose outputs are combined in a well known manner for amplification in apparatus 8 prior to utilization at 9. Utilization apparatus 9 may be a suitable recorder, or another transmitter for retransmitting the received signals as in a relay station. If desired, a suitable automatic gain control circuit, here represented by a condenser I and a resistor II forming a time-constant circuit, may be employed for controlling the gains in the receivers 6 and 'I over leads I2 and I3, respectively. This automatic gain control circuit forms no part of the present invention per se and follows well known practice. It should be understood that the desirable features now employed in the known types of horizontal space diversity receiving systems might also be employed in connection with applicants invention for combining the signal components received over the different antennas and for controlling the gain of the different receivers, as well as for enabling only that receiver which has the largest incoming voltage to control the circuit to the exclusion of the other receivers.

The present invention is believed to find particular application in systems employing frequencies of the order of 100 megacycles and higher. the relaying of signals by radio, for which reason the present invention is useful in a repeater or terminal station of a radio relaying system, As an illustration of a construction which may be employed in the practice of the present invention, the signal collector I might be spaced a distance of about 400 feet above ground, while the signal collector 2 may be spaced a distance of 200 to 300 feet above ground, these collectors being emmegacycles.

Such ultra high frequencies are useful in` signal collectors and 2 are spaced apart from one another vertically at least ten wavelengths apart.

The invention is not limited to the precise arrangement of parts illustrated in the drawing, since various modifications may be made without departing from the spirit and scope of the invention.A For example, it is possible to overcome the type of fading with which the present invention is concerned at frequencies above 30 megacycles by employing a similar arrangement of antennas for transmitting purposes, there being provided means for switching the transmitting apparatus from one antenna to the other vertically spaced antenna, thus providing a different path of travel for the waves from the transmitter to the receiver.

What is claimed is:

1. The method of reducing fading due to atmospheric discontinuities in a radio communication system operating at frequencies above thirty megacycles, which comprises receiving the same signal wave at a plurality of points each spaced vertically apart from the next adjacent one by a distance at least equal to several wavelengths at the operating frequency, and combining the waves received at said points.

2. The method of reducing fading due to atmospheric discontinuities in a radio communication system at frequencies above thirty megacycles which comprises receiving the same signal wave at a plurality of points each spaced apart from the next adjacent one in a vertical direction by a distance equivalent to at least several wavelengths at the operating frequency, and selectively utilizing only the strongest signal re" ceived at said points.

3. A receiving system for reducing or eliminating fading at ultra short wavelengths due to atmospheric discontinuities between transmitter` and receiver comprising a plurality of antennas.,V

each spaced apart from the next adjacent one in a vertical direction by av distance at least equal to several wavelengths at the operating frequency, individual receivers connected to said antennas, and means for combining the outputs of,v

said receivers.

4. A receiving system for reducing or eliminating fading at ultra short wavelengths due to atmospheric discontinuities between transmitter and receiver comprising a plurality of antennas each spaced apart from the next adjacent one in a vertical direction by a distance equal at least. to several wavelengths at the operating frequen-v cy, individual receivers connected to said antennas, and means for selectively utilizing only the strongest signal in the outputs of said receivers.

5. In a radio relaying system for relaying ultra,

high frequency waves of the order of megalengths, and a utilization circuit coupled in common to said receiving antennas.

6. A radio relaying system for relaying ultra high frequency Waves of the order of 100 megacycles and higher, a relaying station having a' plurality of receiving antennas, each antenna being spaced vertically apart from the next adjacent one by a distance at least of the order of ten wavelengths at the operating frequency, and` a utilization circuit coupled in common to said receiving antennas.

7. In a radio relaying system for relaying ultra high frequency waves of the order of 100 megacycles and higher, a relay station having a. plurality of receiving antennas of the electromagnetic horn type mounted on a single mast, each of said antennas being spaced apart vertically from the next adjacent antenna by a distance at least of the order of ten wavelengths at the operating frequency, there being a utilization circuit coupled in common to said antennas.

8. In an ultra short wave radio system, an antenna arrangement for reducing or eliminating fading due to atmospheric discontinuities between the transmitter station and the remote receiver station comprising a plurality of antennas at one of said stations, each of said antennas being spaced apart from the next adjacent antenna in a Vertical direction by a distance at least equal to several wavelengths at the operating frequency, and translation apparatus coupled in common to said antennas. Y

9. In an ultra short Wave radio system, an antenna arrangement for reducing or eliminating fading due to atmospheric discontinuities between the transmitter station and the remote receiver station comprising a plurality of antennas at one of said stations, each of said antennas being spaced apart from the next adjacent antenna in a vertical direction by a distance at least equal to ten wavelengths at the operating frequency, and translation apparatus coupled in common to said antennas.

MARTIN KATZIN. 

